An Input-Series Output-Parallel Modular Three-Phase AC–AC Capacitive-Link Power Converter

Abstract

Modular converters with stackable cells are widely used in high-power applications, where the voltages and/or currents are beyond the ratings of the commercially available switches. Majority of existing modular converter topologies are based on dc-link converters that require several electrolytic capacitors with large capacitances, which reduce the lifetime of the power converter and increase size and volume. This article proposes an input-series output-parallel modular three-phase ac-ac universal power converter, which is formed by three identical and stackable capacitive-link modules that do not require electrolytic capacitors for power conversion. Exclusion of the electrolytic capacitors is achieved by operating the modules in discontinuous capacitor voltage mode. Each module requires two film capacitors with very small capacitances for transferring the power and provides galvanic isolation through high-frequency transformers. Utilization of film capacitors with small capacitances enhances the reliability. Furthermore, the proposed stackable capacitive-link modules enable a scalable and modular design. In this article, power cells are connected in series at the input and in parallel at the output to form a modular universal power converter that can share voltage/current among the power cells in an ac-ac power conversion system. Frequency transformation and voltage step-up/-down are among the other features of the proposed converter. The details of the operation principles along with design considerations are discussed in this article. Moreover, the proposed modular power converter with two power cells is evaluated through simulations and experiments.